The present invention relates generally to the measurement of body composition, and more particularly to a bioelectrical body composition analyzer that displays trend data of one or more body composition factors, such as weight and body fat.
In recent years, there has been an increasing interest among health-conscious individuals to monitor, on a continuing basis, certain of their physical parameters, or attributes, such as their body weight, blood pressure and heart rate. There has also been an increasing interest, particularly among dieters and individuals who engage in exercise or athletic activities, to obtain an accurate determination of the percentage of their weight that is made up of body fat.
It has long been known that the risk of developing certain life-shortening illnesses, such as coronary artery disease, hypertension and diabetes, is related to obesity. It has recently been determined that the health risks associated with obesity are more related to increased body fat than to increased body weight per se. Too little body fat also poses a health risk because the body requires a certain amount of fat for certain normal physiological functions such as cell membrane formation and thermal insulation.
A number of methods are known to determine the body composition in vivo. The most accurate of these are, however, expensive and time-consuming methods such as dual x-ray absorptiometry, dilution techniques and computer topography. These methods, because of their expense and complexity, are not suitable for use in the home or as a consumer device. Other less costly and complex procedures for measuring body fat content are also known.
One such technique, near infrared interaction, is based on the observation that human body fat absorbs light in the near-infrared spectrum. The percent of body fat is calculated from the value of absorbed infrared light in combination with the individual""s height and weight. The main drawback of this technique is that the measurement is made at only one location of the body; its accuracy has also been questioned.
In another known technique to determine body fat content, the thickness of skinfolds formed at defined body sites is measured. The sum of these thicknesses correlates with body fat content. Although this method is one of the most commonly used methods to determine body fat, its use requires a considerable level of skill and training in order to obtain reproducible results. Moreover, since several sites of measurement are very difficult to reach this technique is impractical for use by the person who is trying to make a measurement of his or her body fat.
The use of ultrasound to measure the thickness of the fat layer of the skin, another known technique to measure body fat, involves the reflection of ultrasound waves at the boundaries of the skin layers; the delay of reflected pulses is proportional to that layer of thickness. The major drawbacks in this technique are the need to use fluid for introducing the ultrasound into the skin, the variability of the thickness as a function of pressure and the often observed inaccuracy due to artifacts and reflections at components other than the skin boundaries.
It is known that body fat content as a percentage of total body weight may be measured by measuring the body""s electrical impedance, such as between the individuals feet or between the foot and arm. This technique is known as a bioelectric impedance analysis (BIA). As disclosed in U.S. Pat. No. 5,415,176, body impedance along with the individual""s height and weight can be used to calculate an estimate of the individual""s body density and body fat percentage by the use of a known algorithm that relates body fat to body impedance.
The use of bioelectric impedance analysis to measure body composition, and specifically body fat, is based on the different conductive and dielectric properties of various biological tissues at various frequencies of current. Tissues that contain a lot of water and electrolytes are highly conductive, whereas fat, bone, and air-filled spaces such as the lungs are highly resistive or dielectric tissues. The volume of these tissues can thus be determined from measurements of their combined resistances.
As shown in U.S. Pat. No. 5,415,176, in a typical BIA measurement a pair of electrodes is applied to the individual""s extremities such as the hands or feet. Low-current (less than 1mA) source or generator is applied across a first pair of electrodes, and the voltage across a second pair of electrodes is measured. Since the value of current is known, the voltage drop provides an accurate indication of the body""s impedance. The body impedance, determined in this manner, along with the individual""s body weight and height, can then, as noted, be used to calculate or estimate the individual""s body fat or body density.
Although the knowledge of an individual""s body fat is of considerable value, more useful information in this regard would be an indication of body composition, such as body fat, over time, such as over a period of weeks or months. Such historical information is particularly valuable to individuals who are on a diet or fitness program as an indication of the progress they have made in reducing body fat or weight over a period of time. This trend information allows the individual to better monitor and thus control his or her progress in reducing body fat and body weight by being able to observe the change over time of weight and/or body fat percentage.
A system that provides such a so-called historical or trend display of body weight over a specified period of time is disclosed, for example, in U.S. Pat. Nos. 3,512,592 and 4,301,879. As shown in the latter, weight data from prior measurements are stored in memory and extracted, along with time data, to generate a display that represents the individual""s body weight as a function of time.
The prior body weight trend display systems are, however, complicated to use and provide only limited information with regard to the displayed variations of body weight. Particularly, the known systems are typically usable by only one individual and only provide information on a single aspect of body composition namely body weight. Moreover, the known body measurement and display systems are often not accurate, and the measured data is often not repeatable, because, for example, they fail to take into account variations in body fluid content that occur during the day, and they do not provide averaging of multiple body measurements.
The body composition analyzer of the present invention provides a display of the user""s current body composition parameters such as body fat content or percentage and/or body weight, as well as a display of the prior trend or historical data of those parameters over a period of time. The analyzer base unit, in one embodiment of the invention, includes a set of electrodes connected to a current source to provide an electrical signal representative of the user""s bioelectrical impedance or bioimpedance, which is used to compute the user""s body fat percentage. This information and the user""s measured body weight may be displayed on the base unit and/or transmitted to a remote display unit.
In one embodiment of the invention herein disclosed, the user places the front part of his or her foot on a pair of sensor electrodes and heels on a pair of stimulus electrodes. The measured voltage drop across the sense electrodes is proportional to the impedance (resistance) between the sense and stimulus electrodes, and is indicative of the user""s body fat percentage. A load cell in the base unit produces an additional signal that represent the user""s body weight. The body weight and body fat (impedance) measurement sequence is controlled by a microprocessor that also computes the user""s body fat percentage in accordance with an algorithm stored in its software as a function of the measured bioimpedance along with other factors, such as the user""s height and weight.
The user""s current body fat percentage and body weight data are displayed as a numerical readout, along with graphical trend data of those parameters based on a series of prior measurements of body fat percentage and body weight taken at specified (e.g. weekly or monthly) intervals. Each time a new measurement of body weight and body fat percentage is made, the current data is displayed along with the stored results of prior measurements of those parameters to provide a trend or historical data for the user that indicates how these body composition factors have changed over time.
In a further aspect of the invention, the displayed trend data (e.g. body weight and body fat percentage) are average values of measurements taken during each display interval. Thus, if trend data is displayed for each week, and the user has made two or more measurements in any single week, the values of those measured body weight and body fat percentage measurements are averaged, and the computed average body weight and body fat percentage data are stored in memory for later display.
In a further aspect of the invention, a number of different authorized users may employ the body composition analyzer to display their current and body composition trend data. To this end, an authorized user, before making a new measurement, enters his or her unique identification code so that only previously stored measured body composition data for that user is taken from the memory to create a trend display for that user. Information concerning each authorized user""s height, gender and the like is also stored in memory to allow a computation of, e.g., body fat percentage, to be made for that user.
In yet a further aspect of the invention, measurements of body composition factors taken during certain times of the day outside of a prescribed time interval or window (e.g. in the morning), are displayed, but not stored for inclusion in trend history with other body composition measurements taken during the prescribed time interval. In this manner, the body composition trend data that is displayed is more accurate since it reflects measurements made during the same time of day over a period of weeks or months, and, as a result, is not affected by the normal variations of body fluid content and weight that occur in most individuals during the course of a day.
In a further aspect of the present invention, use of and access to the system by an unauthorized user is prevented by comparing a current body composition measurement for a user who has entered one of the available personal identification codes against stored prior body composition data for the user to whom that identification code has been assigned. If the current measurement deviates from the stored data by a predetermined amount for a given time period, e.g. 5 percent for a one-week interval, the user is identified as being unauthorized and is prevented from gaining access to any of the stored data.
The present invention relates to a body composition trend data analyzer and display system, substantially as defined in the appended claims and as described in the following detailed specification as considered together with the accompanying drawings, in which: